(1) Field of the Invention
The present invention is related to co-agonist peptides of the glucagon and GLP-1 receptors.
(2) Description of Related Art
Pre-proglucagon is a 158 amino acid precursor polypeptide that is processed in different tissues to form a number of different proglucagon-derived peptides, including glucagon, glucagon-like peptide-1 (GLP-1), glucagon-like peptide-2 (GLP-2) and oxyntomodulin (OXM), that are involved in a wide variety of physiological functions, including glucose homeostasis, insulin secretion, gastric emptying, and intestinal growth, as well as the regulation of food intake. Glucagon is a 29-amino acid peptide that corresponds to amino acids 33 through 61 of pre-proglucagon, while GLP-1 is produced as a 37-amino acid peptide that corresponds to amino acids 72 through 108 of pre-proglucagon. GLP-1 (7-36) amide or GLP-1 (7-37) acid are biologically potent forms of GLP-1, that demonstrate essentially equivalent activity at the GLP-1 receptor.
During hypoglycemia, when blood glucose levels drop below normal, glucagon signals the liver to break down glycogen and release glucose, causing blood glucose levels to rise toward a normal level. Hypoglycemia is a common side effect of insulin therapy in patients with hyperglycemia (elevated blood glucose levels) due to diabetes. Thus, glucagon's most recognized role in glucose regulation is to counteract the action of insulin and maintain blood glucose levels.
GLP-1 has different biological activities compared to glucagon. Its actions include stimulation of insulin synthesis and secretion, inhibition of glucagon secretion, and inhibition of food intake. GLP-1 has been shown to reduce hyperglycemia in diabetics. Exendin-4, a peptide from lizard venom that shares about 50% amino acid identity with GLP-1, activates the GLP-1 receptor and likewise has been shown to reduce hyperglycemia in diabetics.
There is also evidence that GLP-1 and exendin-4 may reduce food intake and promote weight loss, an effect that would be beneficial not only for diabetics but also for patients suffering from obesity. Patients with obesity have a higher risk of diabetes, hypertension, hyperlipidemia, cardiovascular disease, and musculoskeletal diseases.
Glucagon is a peptide hormone structurally related to GLP-1 that is well recognized for its acute ability to increase blood glucose through stimulation of glycogenolysis and gluconeogenesis (Jiang & Zhang, Am. J. Physio.l Endocrinol. Metab. 284: E671-E678 (2003)). Of lesser appreciation are the chronic effects of glucagon pharmacology characterized by increases in thermogenesis, satiety, lipolysis, fatty acid oxidation, and ketogenesis (Habegger et al., Nat. Rev. Endocrinol. 6: 689-697 (2010)). Repeated administration of glucagon was first reported decades ago to yield improvements in rodent metabolism, accompanied with lower body weight (Salter, Am. J. Clin. Nutr. 8: 535-539 (1960)). Nonetheless, the inherent risk of hyperglycemia, especially in insulin resistant states such T2DM, has complicated the translation of these observations to human study.
The hormone oxyntomodulin (OXM, glucagon-37) is a posttranslational product of preproglucagon processing in the intestine and central nervous system (CNS) and is secreted from L-cells in the gut in response to food intake. Discovered in 1983, 0) CM has been implicated in the regulation of food intake and energy expenditure (Jarrouse et al., Endocrinol. 115: 102-105 (1984); Schjoldager et al., Eur. J. Clin. Invest., 18: 499-503 (1988)). Central or peripheral administration of OXM in rats causes a decrease in short term food intake with minimal effects on gastric emptying (Dakin et al. Endocrinology, 142: 4244-4250 (2001), Dakin et al. Endocrinology, 145: 2687-2695 (2004)). Repeated intracerebroventricular administration of OXM in rats results in elevated core temperatures and reduced weight gain compared to pair-fed animals, suggesting effects on both caloric intake and energy expenditure (Dakin et al. Am. J. Physiol. Endocrinol. Metab., 283: E1173-E1177 (2002)).
In related studies, peripheral administration of OXM dose-dependently inhibited both fast-induced and dark phase food intake, but unlike GLP-1, had no effect on gastric emptying. OXM also reduced levels of fasting ghrelin and increased c-fos immunoreactivity, in the arcuate nucleus (ARC). Repeated seven-day IP administration of OXM caused a reduction in the rate of body weight gain and adiposity in rats (See Dakin et al. Endocrinology, 145: 2687-2695 (2004)).
Studies of OXM action in mice have demonstrated that although OXM can activate both the glucagon (GCG) and the GLP-1 receptors, the anorectic actions of OXM require only the GLP-1 receptor, as icy OXM inhibits food intake in glucagon receptor knockout mice. However, the anorectic effects of OXM are completely absent in GLP-1 receptor knockout mice. Furthermore, exendin-4, but not OXM, regulates energy expenditure in mice. Hence, OXM appears to be a weak agonist at the GLP-1 receptor, when used in pharmacological concentrations (See Baggio et al., Gastroenterol. 127: 546-58 (2004)). OXM was also found to ameliorate glucose intolerance in mice fed a high fat diet (Dakin et al., Am. J. Physiol. Endocrinol. Metab. 294: E142-E147 (2008) and increase the intrinsic heart rate in mice independent of the GLP-1 receptor (Sowden et al., Am. J. Physiol. Regul. Integr. Comp. Physiol. 292: R962-R970 (2007). OXM has also been shown to differentially affect GLP-1 receptor beta-arrestin recruitment and signaling through Galpha (Jorgensen et al., J. Pharma. Exp. Therapeut. 322: 148-154 (2007)) and to differentially affect hypothalamic neuronal activation following peripheral injection of OXM (Choudhri et al., Biochem. Biophys. Res. Commun. 350: 298-306 (2006)).
In humans, a single 90 minute intravenous infusion of OXM in normal weight healthy subjects reduced hunger scores and food intake at a buffet meal by about 19%. Cumulative twelve-hour caloric intake was reduced by about 11% with no reports of nausea or changes in food palatability (Cohen et al., J. Clin. Endocrinol. Metab., 88: 4696-4701 (2003); Lykkegaard et al., ADA Scientific Sessions, Abstract #1506-P (2003)). More recently, pre-prandial injections of OXM over a four-week period in obese healthy volunteers (BMI about 33) led to a significant reduction of caloric intake on the first day of treatment (about 25%) that was maintained over the course of the study (35% reduction after four weeks) (Wynne et al., Diabetes 54: 2390-2395 (2005)). Robust weight loss was observed at the end of the study in treated subjects (1.9%, placebo-corrected). Plasma levels of OXM were similar to that observed in the infusion study (peak concentration about 950 pM). The absence of any tachyphylaxis and a low incidence of mild and transient nausea (about 3%) despite the relatively high doses necessitated by the poor in vivo stability of OXM (plasma t½<12 minutes) renders this hormone one of the few obesity targets with both human validation and an attractive tolerability profile.
OXM has a very short half-life and is rapidly inactivated by the cell surface dipeptidyl peptidase IV (DPP-IV) (Zhu et al., J. Biol. Chem. 278: 22418-22423 (2002). However, DPP-IV inhibitors are weight-neutral in the clinic, suggesting that supraphysiological levels of OXM (900-1000 pM) may be required to achieve weight loss in humans. OXM peptide analogs for inducing weight loss in humans have been the object of Published International Application Nos. WO03/022304, WO2004/062685, WO2006/134340, and WO2010/096052.
Recently, two independent and simultaneous papers reported the use of relatively balanced GLP-1 receptor/GCG receptor co-agonists as being of enhanced efficacy and safety relative to pure GLP1R agonists in the treatment of rodent obesity, with simultaneous improvement in glycemic control (Day et al., Nat. Chem. Biol. 5: 749-757 (2009); Pocai et al., Diabetes 58: 2258-2266 (2009)). Of related significance is work with oxyntomodulin (OXM), an endogenous precursor to glucagon, which is secreted postprandially by L-cells of the jejuno-ileum together with GLP-1 (Hoist, Regul. Pept. 93: 45-51 (2000); Drucker, Nat. Clin. Pract. Endocrinol. Metab. 1: 22-31 (2005).
Glucagon peptide analogs and derivatives modified to have various degrees of activity at the GLP-1 receptor and GCG receptor have been disclosed in Published International Application Nos. WO2008/1010017, WO2009/155258, WO2011/075393, WO2012/177444, and WO2012/177443. Some of the disclosed glucagon peptide analogs were reported therein to have activity at both the GLP-1 receptor and GCG receptor; however, there remains a need for co-agonist peptides that have activity or potency at the GLP-1 receptor and GCG receptor.